Direct conversion of low power high linearity receiver

ABSTRACT

A radio frequency receiver includes an amplifier and a detector that produces a bias control signal indicating the level of the signal environment in which the receiver is currently operating. A bias generator sets the bias level of the amplifier according to the bias control signal, where the bias level tends to increase as the signal level increases. Further, the receiver, includes a first circuit adapted to receive a radio frequency input signal, the circuit having an adjustable bias level, a bias control having more than one level of control for generating a bias control signal based upon a base-band signal for controlling the first circuit and generating an output signal; and an alternative bypass switch across the first circuit so as to send a DC signal corresponding to the total power generated by said feedback means.

PRIORITY CLAIM

This application is a continuation of U.S. patent application Ser. No.10/051,250, filed Jan. 18, 2002 now U.S. Pat. No. 6,687,491.

FIELD OF THE INVENTION

This invention relates generally to the field of power control for lowpower high linearity receivers. More particularly, this inventionrelates to a direct conversion and in particular, it relates toachieving a low power and high linearity receiver by means of reactivelyadjusting the bias level used by its front-end circuits.

BACKGROUND OF THE INVENTION

An electronic amplifier accepts as its input an electronic signal andproduces as its output a stronger version of that electronic signal. Forexample, recording an electrocardiogram on a chart requires amplifyingthe weak electrical signal produced by a beating heart until the signalis strong enough to move a pen up and down as a paper chart moves pastthe pen.

A linear amplifier is one in which there is a linear relationshipbetween the electronic signal it receives as input and the electronicsignal it produces as output. That is, for a change of X units in itsinput voltage or current, it produces a change in its output voltage orcurrent of k*X (k times X) units for some constant value k, regardlessof whether the value of the input signal is small or large.

Every electronic circuit is unable to produce outputs larger than somelimit. Every electronic circuit is unable to effectively handle inputslarger than some limit or smaller than some other limit. Nevertheless,for many applications of electronic circuits, it is necessary that theybe operated only within a middle range where they produce a linearresponse to changes in their inputs.

Non-linear responses in radio-frequency amplifiers can produce crosstalk or intermodulation between the desired signal and anotherextraneous radio signal that happens to be present at the same time, buton a different frequency or channel. Such undesired signals are calledjamming sources whether or not the interference is intentional. When anamplifier behaves non-linearly, for example, a change of X in its inputsignal produces less than k*X change in its output signal, then theeffect of this non-linearity is to shift the frequency of the signalthat it amplifies. If a desired signal and a jamming source at differentfrequencies are present at the same time (which is typical of theoperating environment for radio receivers), then this frequency shiftresults in cross talk or intermodulation between the two signals.

Many electronic amplifiers electrically combine their input signal witha constant or bias voltage or current. The amount of bias used is chosenin order to set an appropriate operating point for the amplifier. Whenan electronic amplifier is designed, an important choice is whether tomake that constant bias have a relatively large or a relatively smallvalue. The bias value chosen when designing the amplifier can have majorconsequences on how and how well it operates.

One standard technique in designing a linear amplifier is to firstspecify the range of the input signal over which the amplifier mustrespond linearly and the degree to which the amplifier must rejectintermodulation from undesired sources. Then, the amount of bias currentor voltage is set so as to meet to these specifications. The larger therange of linearity desired and the lower the amount of intermodulationthat is acceptable, then the larger the bias must be.

Unfortunately, the larger the bias of an amplifier, the more power itconsumes. Thus, there is a tradeoff between an amplifier's powerconsumption on the one hand and its range of linearity andsusceptibility to intermodulation on the other hand. The design goal ofminimizing power consumption opposes the design goal of maintainingacceptable linearity.

Power conservation is always desirable. But with the advent of widelyused mobile, hand-held and pocket wireless devices, such as pagers andcellular telephones, its importance has increased.

The radio-frequency amplifiers, buffers and other front-end circuitry ina pager or in the receiver section of a cellular or other mobiletelephone must be operating in order for the device to respond to a pageor phone call broadcast to it. Thus, the length of time that a batterywill last while the device is standing by for a page or a phone calldepends on how much power is consumed by its receiver. To manyconsumers, most of the power consumed by the device is consumed instandby mode—for example, a mobile phone may be standing by for a callmany hours each day but in use for calls only minutes each day.

Longer battery life reduces the costs and increases the convenience forconsumers who use, for example, portable devices, including but notlimited to mobile devices, hand held devices, pagers, mobile phones,digital phones, PCS phones and AMPS phones. In these highly competitivemarkets, battery life in standby mode can make the difference as towhich competing product the consumer chooses. Thus, it is critical forthe market success of mobile, portable and hand-held receivers that theyconsume a minimum of power, particularly in standby mode.

The standby battery life of a mobile receiver can be significantlyincreased by lowering its power consumption by lowering the bias levelused in its front-end circuits such as amplifiers and buffers. However,prior art techniques for doing this also reduce the receiver's linearrange and thus increase its susceptibility to intermodulation fromjamming sources.

SUMMARY OF THE INVENTION

Thus, there is a need for amplifiers, buffers and other front-endcircuits for receivers in which power consumption can be decreased infavorable signal environments without reducing linearity or increasingintermodulation susceptibility in adverse signal environments. This needcan be met by means of reactively adjusting the bias level at which suchcircuits operate, i.e. by increasing its bias level in reaction toadverse or strong signal environments so as to allow it to operate usingless power in weaker or typical signal environments.

One embodiment of the invention includes methods and apparatuses areceiver for radio frequency communications, including a first circuitadapted to receive a radio frequency input signal, the circuit having anadjustable bias level, a bias control having a feedback control andhaving more than one level of control for generating a bias controlsignal based upon a signal dependent on baseband circuitry forcontrolling the first circuit and generating an output signal; and abypass switch across the first circuit so as to send a DC signalcorresponding to the total power generated by the feedback control.Thereby an output signal can be generated while signal self mixing orleakages are minimized.

Another embodiment of the invention includes methods and apparatuses forradio frequency generation having a circuit device adapted to receive aradio frequency input signal, the first circuit having an adjustablebias level, a bias control and feedback control having more than onelevel of control for generating a bias control signal based upon abase-band signal for controlling the first circuit and outputting anoutput signal; and a bypass switch across the feedback means adapted toreceive the radio frequency input signal and to output a DC componentsignal corresponding to a bias power received by the first circuit.

Other embodiments of the invention include methods and apparatuses forother reactively biased circuits within a radio frequency receiver,including but not limited to low noise amplifiers, linear amplifiers,mixers and radio frequency to intermediate frequency converters.

Various embodiments of the invention are suitable for use inapplications including but not limited to pager receivers, wirelessInternet receivers, wireless telephone receivers, cellular telephonereceivers, and code division multiple access (CDMA) receivers.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the invention are illustrated in the followingdrawings, in which known circuits are shown in block-diagram form forclarity. These drawings are for explanation and for aiding the reader'sunderstanding. The invention should not be taken as being limited to theembodiments and design alternatives illustrated.

FIG. 1 shows the building blocks, or functional components, that make upone embodiment of the invention. This embodiment is a receiver amplifierthat adjusts its own bias level in reaction to the current signalstrength within its environment. It also shows the interconnections ofthese functional components.

FIG. 2 shows electronic circuit components and their interconnectionsthat can be used to make each of the functional components shown in theprevious figure. The embodiment of the invention shown is suitable forsmall signal or low noise applications. Also, this embodiment issuitable for a modular, multi-stage embodiment of the invention. Thefunctional component shown as variable resistance 204-A in FIG. 2( a)can be replaced with variable resistance 204-B in FIG. 2( b) or withvariable resistance 204-C in FIG. 2( c).

FIG. 3 shows the electronic circuit components and theirinterconnections for another embodiment of the invention, specifically asimplified self-adjusting RF amplifier.

FIG. 4 shows the electronic circuit components and theirinterconnections for an embodiment of the invention, specifically aself-adjusting IF amplifier.

FIG. 5 shows the functional components and their interconnections foryet another embodiment of the invention. This embodiment is the firststages of a receiver within a mobile device such as a cellulartelephone. This embodiment has multiple stages of amplification and onestage of frequency conversion, where each stage self-adjusts its ownbias level. FIG. 5 also shows the functional components and theirinterconnections for an embodiment of the invention in a transceiver,i.e. a device that both transmits and receives.

FIG. 6 shows the functional components and their interconnections foranother embodiment of the invention. This embodiment is the first stagesof a receiver with multiple stages of active circuits such asamplifiers, where the bias level used within each stage is adjusted by asingle signal level detector and a single bias adjustment circuit.

FIG. 7 shows the functional components and their interconnections foranother embodiment of the invention. This embodiment is the first stagesof a receiver in which a first filter and an RF amplifier are optionallyincluded in the receiver's signal path or switched out of it.

FIG. 8 shows electronic circuit components and their interconnectionsthat can be used to make another embodiment of the invention that uses asample and hold circuit that can improve the accuracy of the reactivebias function by compensating for variations in the threshold of circuitcomponents.

FIG. 9 shows how one embodiment of the invention can be made with manyof its electronic circuit components formed using a single integratedcircuit with 10 pins.

FIG. 10 shows the functional components and their interconnections foranother embodiment of the invention. This embodiment is the first stagesof a receiver that uses the integrated circuit of the previous figure tobuild a receiver that can be operated in several modes used in mobiletelephone applications. These modes include analog modes such ascellular and advanced mobile phone service (AMPS) as well as digitalmodes such as code division multiple access (CDMA) and personalcommunication service (PCS).

FIG. 11 show the functional components and their interconnection foranother embodiment of the invention. This embodiment is the directconversion of the front end bias control that is controlled by the RSSIsignal.

FIG. 12 shows the functional components and their interconnection foranother embodiment of the invention. This embodiment is the directconversion of the front end LNA connected to the active mixer.

FIG. 13 direct conversion stage by stage from the input to the outputspectrum in an embodiment of the present invention.

FIG. 14 shows a three dimensional diagram of the power control and thejamming power in an embodiment of the present invention.

DETAILED DESCRIPTION

Disclosed herein are various alternative embodiments of and alternativedesigns for the invention. The invention, however, should not be takenas being limited to the embodiments and alternatives described. Oneskilled in the art will recognize still other alternative embodimentsand designs, as well as various changes in form and detail. These may beemployed while practicing the invention without departing from itsprinciples, spirit or scope.

FIG. 1 is a functional block diagram of receiver amplifier 100 accordingto one embodiment of the invention. This amplifier has reactive biasing,i.e. it adjusts its bias level in reaction to the signal strength withwhich it is currently operating.

RF/IF receiver amplifier 101 amplifies input signal 120 into outputsignal 121. The bias of amplifier 101 is set by bias level 143, which isproduced by bias generator 103.

RF/IF receiver amplifier 101 can be any type of linear amplifier withcharacteristics suitable for radio-frequency (RF), intermediatefrequency (IF), or other applications. RF/IF receiver amplifier 101 canbe, but is not limited to, a common emitter amplifier, a common baseamplifier, a common collector amplifier, a voltage amplifier, a currentamplifier, a transconductance amplifier, a transresistance amplifier, anamplifier with feedback, or an amplifier without feedback. In someembodiments of the invention, reactive biasing is applied only to RFstages, or only to some of the initial RF stages, and the bias levels onIF stages are fixed according to conventional techniques.

As shown in FIG. 1, level detector 102 detects the signal level of RF/IFoutput signal 121, and thus it indirectly detects the signal level ofRF/IF input signal 120. Alternatively, level detector 102 can directlydetect the signal level of RF/IF input signal 120 or of an intermediatesignal between the input and the output signal. Level detector 102produces bias control signal 140 according to the signal level that itdetects.

Level detector 102 can be any type of circuit that is able to detectchanges, over an appropriate time frame, in the signal level with whichthe receiver is currently operating. For example, level detector 102 canbe a rectifier, or a heat generator of some type coupled to a heatmonitor such as a thermsistor.

The detected signal level can indicate an averaged signal level thatdepends on the signal environment in which the receiver is currentoperating, with the average being taken over a suitable period of time.Generally, the frequency of bias level 143 should be limited to beorders of magnitude lower than the frequency of the signal of interest.As a first example, a 2 MHz response in bias level may provide anappropriate time frame over which to average the signal level and adjustthe bias level for a 2 GHz carrier signal such as is used in acode-division multiple access (CDMA) signal.

Also, consideration should be given to the possibility of spurioussidebands arising between the bandwidth of the bias level transferfunction and the bandwidth of the signal of interest. To continue withthe CDMA example where the desired CDMA signal has a bandwidth limitedto 1.25 MHz, a response in bias level limited to being near 2 MHz maykeep any such sidebands out of the receiver's bandwidth, and thusminimize interference with the CDMA signal.

Alternatively, the response in bias level could be limited to beingbelow the receiver's bandwidth. As a second example, a 100 Hz biasadjustment response may minimize interference with a voice signallimited to between 500 and 3,000 Hz. However, limiting the frequency ofbias level 143 to be below the range of the signal of interest mayundesirably slow down the response time of the receiver to changes insignal strength. This could be significant to system performance if thecurrent signal environment includes a jamming signal that is onlyintermittently present.

Thus, bias level 143 should be able to vary quickly enough that theperformance of the overall system in which the reactively biasedamplifier is used is not harmed by a lag or hysteresis effect, such asmight occur when a high-signal environment changes to a low-signalenvironment, or visa versa.

Bias generator 103 produces bias level 143 according to the appropriatebias control signal. If bias adjustment circuit 105 is used, then biasgenerator 103 varies bias level 143 according to adjusted bias controlsignal 141, otherwise bias control signal 140 is used. Bias generator103 can be any circuit that varies bias level 143 within a target rangeaccording to the appropriate bias control signal.

In amplifiers with reactive biasing, level detector 102 and biasgenerator 103 to operate such that the bias applied to RF/IF receiveramplifier 101 tends to increase as the input/output signal levelsincrease, i.e. as the receiver is used in an environment having strongersignal conditions. However, this increase need not be a linear or evenmonotonic increase. In some designs, the bias level may only generallytend to increase as the signal level increases. Preferably, this generaltendency to increase is sufficient to keep RF/IF receiver amplifieroperating with sufficient linearity and intermodulation rejection forthe particular application.

In embodiments of the invention that use bias adjustment circuit 105, itadjusts, filters, amplifies and/or conditions bias control signal 140into adjusted bias control signal 141, which is then used by biasgenerator 103 to generate bias level 143. The adjustment or adjustmentsapplied may include any transfer function, preferably but notnecessarily monotonic, including but not limited to conditioning,filtering, clipping, expanding, amplifying, dampening, scaling,offsetting, band limiting, sampling and holding and/or summing with anDC offset.

Bias adjustment circuit 708 can also include circuitry that compensatesfor threshold variations of active devices within the reactive biasingsystem, including but not limited to variations in the threshold of itsfield effect transistors (FETs). Because the linear range of a FET maybe narrow, it may be important to calibrate or set the levels used so asto maintain the circuit's operation within that linear range.

Bias adjustment circuit 105 could be any circuit that produces adjustedbias control signal 141 as a function of bias control signal 140. Ifregulating feedback signal 142 is used, then bias adjustment circuit 105can also vary bias level 143 according to regulating feedback signal142.

Various embodiments of bias adjustment circuit 105 include but are notlimited to circuitry that conditions bias control signal 140, that scaleit, that compare it against a reference level, that samples and holdsappropriate levels so as to calibrate a reference level corresponding toa given signal environment (such as an environment that is relativelyfree of jamming signals). Other embodiments include combinations of suchcircuitry.

In embodiments of the invention that use variable resistance 104, it canfunction as a circuit element within bias generator 103. By varying itsresistance, variable resistance 104 alters bias level 143. Variableresistance 104 could be any circuit that varies its resistance as afunction of control signal 140, or of adjusted bias control signal 141when available. Variable resistance 104 can be employed within biasgenerator 103 so as to vary the current of bias level 143, so as to varythe voltage of bias level 143, or both.

In embodiments of the invention that use bias feedback signal 142, itcan simply be bias level 143, or it can be a signal derived from biaslevel 143 or a signal that is a predecessor of bias level 143. Its useis optional, but it increases the stability of bias level 143,particularly when the circuit is operated under a wide range of voltageor temperature conditions, or when manufacturing tolerances of biasgenerator 103 or of other portions of the receiver have a significantimpact on bias level 143 or on what bias level 143 should be set to.Embodiments of the invention that use bias feedback signal 142 can alsobe somewhat self calibrating as to the amount of variation produced inbias level 143.

In some embodiments of the invention, the distinctions between leveldetector 102, bias adjustment circuit 105 and bias generator 103 breakdown and particular circuit components operate to produce multiplefunctions.

It is possible, and may be desirable in some applications, for onedetector to provide a bias control signal to multiple conditioners, orfor one bias adjustment circuit to provide a bias control signal tomultiple bias generators.

Reactive biasing allows amplifier 100 to be designed such that its powerconsumption in typical signal environments is decreased without reducingits linearity or intermodulation immunity in strong signal environments.Amplifier 100 can be designed with a bias level that is low, relative tothe maximum signal environment it might be used in. Then, when it isused in a strong signal environment, it adjusts its bias upwards, whichincreases its linearity and intermodulation immunity during the periodof time that the strong signal environment is present.

Such a linear amplifier with low power consumption in typical signalenvironments is particularly advantageous for mobile, hand held orpocket devices such as pagers, telephones or wireless data connections.With the advent of such devices, it has become critical to design linearamplifiers that consume as little power as possible while waiting for asignal that is addressed to them. This waiting mode may dominate theusage cycle of such devices, thus power savings during this mode mayhave a significant impact on battery life.

The RF and IF amplifiers in a cellular telephone, pager or data receivermust be operating in order for the device to respond to a phone call,page, e-mail or other transmission that is broadcast to them. Thus, thelength of time that a battery will last while the device is standing byfor a transmission addressed to the device depends on how much power isconsumed by the amplifiers and other circuits in its receiver section.

The power consumption of some mobile devices can be significantlyreduced by using amplifiers, buffers, mixers and other circuits thatembody the invention in the mobile device's receiver. In someapplications, the invention significantly increases the length of timethat a battery lasts when the mobile device is in standby mode.

Many mobile devices are in standby mode much of the time. For example, amobile telephone user may have their phone on ten hours a day, of whichonly ½ hour is spent actually using a phone connection. In this case,their cellular, PCS, amps or other mobile phone spends 9½ hours a dayonly receiving, i.e. listening for a call directed to them, and ½ hourper day both receiving and transmitting. In such a usage pattern, thephone's receiver section is active 19 times longer than its transmittersection. Thus, receiver power reduction can substantially reduce havingto change or recharge batteries or other energy storage devices in themobile device, which can produce a corresponding gain in userconvenience and reduction in user expense.

In some embodiments of the invention, reactive biasing can allow linearamplifier 101 to be designed such that its linearity and intermodulationimmunity are increased. When such an amplifier is used in a strongsignal environment, it adjusts its own bias upwards, thus increasing itslinearity and intermodulation immunity. Rather than utilizing reactivebiasing for reducing the receiver's power consumption, these embodimentsof the invention utilize it for increasing the receiver's range oflinearity.

FIG. 2 is a circuit diagram of a small-signal or low-noise radiofrequency (RF) reactively biased receiver amplifier according to oneembodiment of the invention.

FIG. 2( a) shows the amplifier's components partitioned into functionalblocks corresponding to those shown in the previous figure. Thoseskilled in the art will recognize that there are numerous ways ofimplementing each of these functional blocks and that other ways will bedeveloped. These are all within the principles, spirit and scope of theinvention.

The variable resistance block within amplifier 200 can be implemented invarious ways, including but not limited to variable resistance 204-A,shown in FIG. 2( a), variable resistance 204-B, shown in FIG. 2( b), andvariable resistance 204-C, shown in FIG. 2( c).

The components of the amplifier of FIG. 2, their preferred values andtheir functional descriptions are given by the following table:

TABLE 1 Components of Low Noise, Reactively Biased RF AmplifierReference Designator Suite Value Function RF Amplifier 201 C1 ~1.0–22 pFRF tuning and DC block capacitor C2 ~10–1000 pF RF decoupling capacitorC3 ~1.0–22 pF RF tuning and DC block capacitor C4 ~10–1000 pF RFdecoupling capacitor L1 ~1.5 to 22 nH RF tuning and DC bias feedinductor L2 ~1.5 to 22 nH RF tuning and DC bias feed inductor R1 0 to 27ohm Lossy resistance to aid stability Q1 RF frequency, high linearityField Effect Transistor (FET), low noise preferred Detector 202 C5 ~1–22pF Provides DC blocking and RF coupling between the output of RFamplifier 201 and level detector 202. The smaller its value, the lessthe coupling. C6 ~22–100 pF RF decoupling capacitor D1 Rectificationdiode chosen for desired detector characteristics D2 Rectification diodechosen for desired detector characteristics L3 ~22–39 nH RF choke BiasConditioner 205 C7 27–1000 pF Capacitor to set the time constant (or thecut off frequency) of the bias control signal U1 Op amp chosen forsignal swing range and response time characteristics R2 ~1–100K ohmResistor to set the gain/ scaling for the bias level conditioning R3~1–100K ohm Resistor to set the gain/ scaling for the bias levelconditioning Not shown Diodes may be optionally used for shaping theinput/ output characteristic of this stage Variable Resistance 204 Q3Field effect transistor (FET) chosen for its characteristic ofdrain-source resistance versus bias R4 ~51–100K ohm Resistor to scalethe variable resistance network R5 10–~51K ohm Resistor to scale thevariable resistance network Bias Generator 203 Q4 Dual PNP biastransistor R6 ~2.7 to 10K ohms Sets current on left PNP transistorwithin Q4, helps set how much Q1's bias varies with signal strength R7~10 to 100 ohms Sets DC bias through Q1 R8 ~10 to 100K ohms Aidsstability of DC bias network R9 ~10 to 100K ohms Aids stability of DCbias network

The use of op amp U1 or of any type of active amplification in the biascontrol path, adds cost, complexity and power consumption to thereceiver. Nevertheless, U1 can support several potentially advantageousfeatures of this embodiment of the invention.

One advantage of using an op amp is that relatively precise control canbe obtained over the bias level and the gain, limiting, filtering andhysteresis of its adjustment.

Also, by using an op amp such as U1, feedback can be used to compensatefor variations due to temperature changes or component tolerances. Thisfeedback could be directly from the bias current in the amplificationdevice, such as by sensing the voltage drop across R7.

Another way to obtain such precision is via digitizing the detectedsignal level. The digital signal level can be used as an index into alook-up table, which can contain a precisely calibrated digital biaslevel for each digital signal level. The digital bias level can then beconverted back into an analog bias level.

Another advantage of using an op amp such as U1 is that it provides anamplification element in the bias control path.

One factor that should be considered in the design of a reactivelybiased RF amplifier is that non-lineaty in the RF front end of areceiver can have a significant system impact at fundamental peak signallevels that are very small. These peak signal levels may be much smallerthan the bias level of the RF amplifier. U1's amplification of therelatively small detected signal level allows the bias level of the RFamplifier to vary over an appropriate range.

Another factor that plays an important role in the design of reactivelybiased RF amplifiers according to the invention is the measure ofintermodulation known as the IIP³, or the third-order inputintermodulation product. If an amplifier is non-linear, then the energyof the input signal is shifted into harmonics of the frequency of theinput signal. If two signals at different frequencies are present in asignal amplified non-linearly, then these harmonics intermodulate or mixto produce intermodulation products, i.e. multiple frequencies at thesum and difference of all of the frequencies present. If these productsfall within the bandwidth of the signal of interest and have sufficientamplitude, then the usability of the receiver deteriorates. The IIP³ isa measure of the amplitude of these intermodulation products.

A receiver's IIP³ can be estimated by one skilled in the art based onits circuit configuration and component values. Also, it can bedetermined via a circuit simulation based on a hypothetical signalenvironment, i.e. the signal strength, frequency and bandwidth of thedesired signal and of any jamming or extraneous signals. Also, it can bemeasured based on the performance of an actual prototype or productionreceiver.

Yet another design factor to be considered is cross talk, i.e. where thetransmitted signal from a transceiver enters its received signal pathand becomes part of the receiver's signal environment. The designdetails of how to reduce the adverse affects of cross talk withappropriate filtering will be easily determined by one skilled in theart, where the filtering is between the transmitter section and thereceiver, within the receiver section, or both.

Nevertheless, cross talk can interact with intermodulation. Thisinteraction can be difficult to predict via static calculations. Theseinteractions can be examined by one skilled in the art, by means ofdynamic simulation of the circuit design using realistic models ofsignal environments, perhaps based on target specifications forintermodulation rejection. They can also be examined by experimentaltesting of bread boards of the circuit design and of prototypetransceivers or production transceivers. Because reactively biasedamplifiers dynamically vary their intermodulation rejection, suchsimulations and testing can play an important role in determining howmuch to vary the bias level in different signal environments.

Another design factor to be considered is that the target specificationspublished for receivers do not take into account the effects of reactivebiasing. Published specifications may assume that a high-noiseenvironment is the worst case for a receiver; thus, they may onlyspecify target intermodulation parameters under such conditions. Areactively biased receiver could operate well under the published testconditions because it detects the strong signal environment and ups itsbias levels accordingly. However, it is possible for that same receiverto have problems in the presence of intermediate levels of jammingsignals (or even under low levels of jamming signals) if it is tooaggressive about lowering its bias levels under such conditions.

Thus, a reactively biased receiver should be designed for and testedover the entire range from high levels of jamming signals to minimal ornon-existent jamming signals.

Another design factor to be considered is a possible effect on the gainof the amplifier when its bias level is reactively adjusted. It may bedesirable to select the range of bias level and other characteristics ofthe amplifier such that there is little if any change in its gain as itis reactively biased. One benefit of such an approach is that it may bedesirable to keep the amplifier operating at or near maximum gain,particularly if the amplifier is early in the front end of the receiverwhere the signal strengths are low.

Another benefit of this approach is that it minimizes the possibility ofa positive feedback loop with respect to the receiver's gain. The gainfeedback loop arises as follows: a stronger signal level being detectedincreases both the bias level and the gain of the amplifier, then astill stronger signal level will be detected, which will again increasethe bias level and again increase the gain, etc. If such a change ingain of 1 dB (for example) results in a subsequent change in gain ofsubstantially less than 1 dB, then this feedback effect will stabilize.In this case, this feedback effect can have a desirable effect on theshape of the transfer function over the bias range—for example, it mayreduce or eliminate the need to amplify or condition the bias controlsignal.

On the other hand, if a change in gain of 1 dB (for example) results ina subsequent change in gain near, or more than 1 dB, then this feedbackeffect will not stabilize. Thus, the reactive biasing and perhaps thereceiver itself will not operate properly.

FIG. 3 is a circuit diagram of a simplified RF amplifier, according toone embodiment of the invention. This circuit avoids the costs,complexity and power consumption of the op amp of the circuit of FIG. 2.This is a significant reduction. In terms of circuit area for animplementation on a monolithic integrated circuit and in terms of powerconsumption, U1's area and power requirements might be on the order ofthose of all of the rest of FIG. 2's circuitry put together.

This embodiment also blurs the distinctions among the functional blocksshown in FIGS. 1 and 2 in that several of this circuit's componentsaffect how the circuit functions in multiple ways that cross theboundaries of these functional blocks.

The components of the self-adjusting, reactively biased RF amplifier ofFIG. 3, their suitable values and their functional description are givenby the following table:

TABLE 2 Components of Simplified, Reactively Biased RF AmplifierReference Designator Suitable Value Function C1 ~0.1 uF Helps set thetime constant of the detector circuit. Also provides RF decoupling. C2~22 pF Provides RF bypass to prevent RF feedback C3 ~22 pF Optional.Provides RF bypass at the source of Q1. C4 ~22 pF Provides DC blockingand impedance matching for the detector circuit C5 ~2–22 pF Provides DCblocking and impedance matching for the input of the amplifier C6 ~2–22pF Provides DC blocking and impedance matching for the output of theamplifier C7 ~22 pF Provides RF bypass at the emitter of Q2 D1 SchottkeyRectification diode for the detector circuit D2 Schottkey pair Voltagedoubler diode and return path for the detector current L1 ~6.8 nH RFchoke and load matching inductor L2 ~4.7 nH Output matching inductor R2~1K ohms Sets bias of the detector circuit R3 ~5K ohms Sets timeconstant and bias voltage of the detector circuit R4 ~30K ohms Optional.Scales the bias level R5 ~50K ohms Sets bias feedback for Q1. Also aidsin conditioning the bias control. Also helps set the bias level. R610–20K ohms Operates with R7 to set bias feedback for Q2 R7 ~10K ohmsSets feedback for both Q1 and Q2. Also helps set the bias level. R8 ~10ohms Part of bias feedback for Q1. Also helps set the collector bias forQ2 R9 ~140 ohm Scales the variable resistance of Q1 R10 0–~10 ohmsOptional. Sets collector bias of Q2 without providing feedback on Q1 R110–~20 ohms Optional. Provides Q2 emitter stabilization resistance Q1N-channel power FET Biasing transistor configured to form a variableresistance circuit Q2 Bipolar RF transistor Amplifying transistor

One factor that should be taken into consideration in the design of areactively biased RF amplifier according to the invention is that thenon-linearity in the RF or front end of a receiver can have asignificant system impact at fundamental peak signal levels much smallerthan the bias level of the RF amplifier. Therefore, it is desirable thatthe detector be able to sense a small signal and apply enough biascontrol to accommodate this signal condition. One way this can be doneis for matching elements to be added at the detector's input, which arecoordinated with the matching elements at the amplifier's output. Whilethis can be an effective technique in some situations, activeamplification along the lines of the previous figure may be required insome low-noise or small-signal applications.

FIG. 4 is a circuit diagram of a self-adjusting, reactively biasedintermediate frequency (IF) amplifier according to one embodiment of theinvention.

Its components, their preferred values and their functional descriptionsare given by the following table:

TABLE 3 Components of Reactively Biased IF Amplifier ReferenceDesignator Suitable Value Function C1 ~0.1 uF Sets the time constant ofthe detector circuit C2 ~100 pF Provides IF bypass to prevent IFfeedback C3 ~100 pF Optional. Provides IF bypass at the source of Q1. C4~100 pF Provides DC blocking and impedance matching for the detector.However, without C4, the DC present could be used to bias the detector.C5 ~2–22 pF Provides DC blocking and impedance matching for the input ofthe amplifier C6 ~2–22 pF Provides DC blocking and impedance matchingfor the output of the amplifier C7 ~100 pF Provides IF bypass at theemitter of Q2 D1 Schottkey Rectification diode for the detector circuitD2 Schottkey pair Optional. Accelerates the response of the system tochanges in signal conditions at the high end L1 ~560 nH IF choke andload matching inductor L2 ~330 nH Output matching inductor L3 22–39 nHRF choke R0 ~30K ohms Optional. Establishes an active bias for thedetector circuit, which may or may not be desired R1 ~100K ohmsOptional. Scales the IF input to the detector R2 ~30K ohms Optional.Scales the IF input to the detector R3 ~5K ohms Optional. Establishes aDC return path and sets a leakage bias for the detector R4 ~30K ohmsOptional. Scales the bias level R5 ~50K ohms Sets bias feedback for Q1and sets the time constant of the detector R6 ~10–20K ohms Operates withR7 to set bias feedback for Q2 R7 ~10K ohms Sets feedback for both Q1and Q2 R8 ~10 ohms Part of bias feedback for Q1. Also helps setcollector bias for Q2 R9 ~140 ohm Scales variable resistence of Q1 R100–~10 ohms Optional. Sets collector bias of Q2 without providingfeedback on Q1 R11 0–~20 ohms Optional. Provides Q2 emitterstabilization resistance Q1 N-channel power FET Biasing transistorconfigured to form a variable resistance circuit Q2 Bipolar IFtransistor IF amplifying transistor

In an alternative embodiment of a reactively biased IF amplifieraccording to the invention, R0 could provide the detector bias.

One factor that should be taken into consideration in the design of areactively biased IF amplifier according to the invention is that itslinearity requirement may not be as great as for a front-end RFamplifier; that is, a substantially stronger jamming signal may berequired at IF stages to produce undesirable amounts of intermodulation.Therefore, the relative range of adjustment in the bias levelappropriate for an IF amplifier may be smaller than for an RF amplifier.

Another factor that should be taken into consideration in the design ofa reactively biased IF amplifier according to the invention is that thesignal strength of its output may be substantially higher than for an RFstage. Therefore, it may be possible for its output signal to be scaled,rectified and the resulting signal scaled again. This can allow the IFamplifier to be self-adjusting according to the transfer functiondesired. In contrast, the relatively weak signals at the RF level maynot allow such two-stage scaling.

FIG. 5 shows the application of one embodiment of the invention in atransceiver application, such as but not limited to a mobile phonedevice or a two-way pager. In transmitter section 550, final poweramplifier 503 provides an RF transmission signal to antenna 501, viaantenna signal line 521 and duplexer 502. Duplexer 502 can be a filter,or set of filters, that allows the RF energy output of final poweramplifier 503 to be coupled to antenna 501 while filtering this energyto reduce the amount of it that enters the receiver section of thedevice.

FIG. 5 is also a functional block diagram of the front end of areceiver, according to one embodiment of the invention, with multiplestages of amplification, each stage having self-adjusting reactivebiasing. Receiver section 551 receives RF input signal 523 from antenna501 via duplexer 502. It produces IF output signal 533. As shown, it hasfour stages of active circuitry, each with self adjusting bias; however,other embodiments can have more or fewer active circuit stages. Also inyet other embodiments, some of the active circuits can have a fixedrather than self adjusting bias, or commonly controlled bias levels.

Receiver section 551 is not a complete receiver; however, the designdetails of other circuitry required for a specific application of theinvention will be easily determined by one skilled in the art. It mayinclude but not be limited to a local oscillator, local oscillatorbuffer, IF to audio/digital converter, audio/digitalamplification/processing, automatic gain control, user interface, andaudio/video input/output.

Initial low-noise amplifier 504 receives RF input signal 523 andproduces internal RF signal 525. The bias of initial low-noise amplifier504 can be set by first self-adjusting bias level 524, which can beproduced internally to initial low-noise amplifier 504 (as shown) or canbe produced based on internal RF signal 525.

Initial low-noise amplifier 504 can be any type of RF amplifier withcharacteristics suitable for the particular application. In particular,initial low-noise amplifier 504 can be the RF amplifier shown in FIG. 2,or a variation thereof. Bias adjustment circuit 205, which includesop-amp Q2, allows this amplifier stage to re-actively bias according tochanges in the relatively low signal levels at the initial RF stage of areceiver. That is, relatively small changes in RF signal levels of RFinput signal 523 can be amplified by op-amp Q2 to produce adjustments infirst self-adjusting bias level 524 that are large enough that thelinearity/intermodulation rejection of initial low-noise amplifier 504can be preserved in high-signal environments.

Filter 505 receives internal RF signal 525 and produces internal RFsignal 526. Filter 505 can attenuate out of band components within theRF signal, including but not limited to any leakage (through duplexer502) of transmission energy into the receiver section.

Second RF amplifier 506 receives internal RF signal 526 and producesinternal RF signal 528. The bias of second RF amplifier 506 can be setby second self-adjusting bias level 527, which can be producedinternally to second RF amplifier 506 as shown or which can be producedbased on internal RF signal 526 or 528.

Second RF amplifier 506 can be any type of RF amplifier withcharacteristics suitable for the particular application. In particular,second RF amplifier 506 can be the RF amplifier shown in FIG. 3, or avariation thereof. While the bias adjustment conditioning function inthis receiver does not include an op-amp, the position of this amplifieras the second stage within the receiver gives this amplifier stage ahigher signal level to work with. Therefore, this second RF stage may besensitive enough to appropriately adjust its bias without the addedcost, complexity and power consumption of an op-amp.

RF to IF converter 507 receives internal RF signal 528 and producesinternal IF signal 530. The bias of RF to IF converter 507 can be set bythird self-adjusting bias level 529, which can be produced internally toRF to IF converter 507 as shown or which can be produced based oninternal RF signal 528 or internal IF signal 530.

RF to IF converter 507 can be any type of RF to IF converter or mixerwith characteristics suitable for the particular application.

IF amplifier 508 receives internal IF signal 530 and produces internalIF signal 532. The bias of IF amplifier 508 can be set by fourthself-adjusting bias level 531, which can be produced internally to IFamplifier 508 or which can be produced based on internal RF signal 530or internal IF signal 532.

IF amplifier 508 can be any type of IF amplifier with characteristicssuitable for the particular application. In particular, IF amplifier 508can be the IF amplifier shown in FIG. 4, or a variation thereof. This IFstage may be sensitive enough to appropriately adjust its bias withoutthe added cost, complexity and power consumption of an op-amp.

Filter 509 receives internal IF signal 532 and produces IF output signal533. Filter 509 can attenuate out of band components within the signal.

As shown, each active stage in receiver section 551 has its own selfadjusting bias level. Substantial reductions in the use of receiverpower in some signal environments can be achieved by the embodiment ofthe invention shown in FIG. 5. For example, to the extent that energyfrom jamming sources (including but not limited to energy leaked fromfinal power amplifier 503 via duplexer 502) is attenuated by filteringbetween active stages, then stages after the filtering can operate atreduced bias levels and at reduced power consumption relative to thestages prior to the filtering. Nevertheless, some of the active stageswithin receiver section 551 could be implemented with fixed bias levels,or with bias levels subject to a common control.

FIG. 6 is a functional block diagram of a receiver front end, accordingto one embodiment of the invention, with multi-stage reactive biasingthat has a common control. It differs from the embodiment of theprevious figure in that all active stages with reactive biasing operateat the same relative bias level depending on the strength of the currentsignal environment. It also differs from the previous figure in that thebias level of local oscillator & buffer 624 is adjusted in reaction tosignal level.

FIG. 6 is a functional block diagram of receiver front end 600. Receiverfront end 600 receives RF input signal 631 from antenna 601 and producesIF output signal 635. As shown, it has five stages of active circuitry,each with reactively adjusted bias. However, other embodiments can havemore or fewer active circuit stages, or some of the active circuits canhave a fixed rather than a reactively adjusted bias, or some of theactive circuits can have a self adjusting bias.

Receiver front end 600 is not a complete receiver; however, the designdetails of other circuitry required for a specific application of theinvention will be easily determined by one skilled in the art. It mayinclude but not be limited to an IF to audio/digital converter,audio/digital amplification/processing, automatic gain control, userinterface, and audio input/output.

First RF amplifier 602 amplifies RF input signal 631 into internal RFsignal 632. The bias of first RF amplifier 602 can be set by bias level642, which can be produced by first bias generator 612. First RFamplifier 602 can be any type of RF amplifier with characteristicssuitable for the particular application. For example, it can be RFamplifier 201 as shown in FIG. 2( a).

Second RF amplifier 603 amplifies internal RF signal 632 (which can bedirectly as generated by first RF amplifier 602 or after suitablefiltering) into internal RF signal 633. The bias of second RF amplifier603 can be set by bias level 643, which can be produced by second biasgenerator 613. Second RF amplifier 603 can be any type of RF amplifierwith characteristics suitable for the particular application. Forexample, it can be the RF amplifier shown in FIG. 3.

RF to IF converter 604 converts internal RF signal 633 into internal IFsignal 634. RF to IF converter 602 can be any type of RF to IF converteror mixer with characteristics suitable for the particular application.

IF frequency signal 654 can be produced by local oscillator & buffer624. The bias used in local oscillator & buffer 624 can vary in reactionto the strength of the signal environment in which the receiver iscurrently operating. The bias level used by local oscillator & buffer624 can be bias level 644, which can be generated by third biasgenerator 614.

Local oscillator & buffer 624 can be any type of an oscillator and/orbuffer that can produce IF frequency signal 654. In some embodiments,the local oscillator portion produces a signal at the chosen IFfrequency, and the active stage that amplifies and/or buffers this IFsignal prior to its use in RF to IF converter 604 can use adjustablebias level 644.

Such reactive biasing of the local oscillator & buffer is like thereactive biasing of the RF and IF amplification stages in that it isdone in order to save power in typical signal environments, i.e., thosein which the extraneous or jamming signals are not as strong as they areunder worst-case operating conditions. However, such reactive biasingdiffers from that of the amplifier stages in that it operates by varyingthe compression point and perhaps the gain of local oscillator 624, orof the buffer/amplifier stage within local oscillator 624. The designdetails of local oscillator and buffer 608 will be readily determined byone skilled in the art. In contrast to reactively biased amplificationstages, it may be preferable to choose a bias level range and otherparameters for local oscillator and buffer 624 such that any change ingain is low or minimal.

IF amplifier 605 amplifies internal IF signal 634 into IF output signal635. The bias of IF amplifier 605 can be set by bias level 645, whichcan be produced by fourth bias generator 615. IF amplifier 605 can beany type of IF amplifier with characteristics suitable for theparticular application. For example, it can be the IF amplifier shown inFIG. 4.

As shown in FIG. 6, level detector 606 receives IF output signal 635. Itdetects the signal level of IF output signal 635, and thus indirectly itdetects the signal level of RF input signal 631. In other embodiments,level detector 606 can receives a signal that is intermediate between RFinput signal 631 and IF output signal 635. According to this signallevel, level detector 606 produces bias control signal 636.

Level detector 606 can be any type of circuit that is able to detectchanges in the average input and output signal levels that occur over asuitable time frame. In particular, it can be level detector 202 asshown in FIG. 2( a) with suitable modifications to adapt the circuit toIF frequencies.

Bias adjustment circuit 607 produces adjusted bias control signal 637according to bias control signal 636. Bias adjustment circuit 607 can beany circuit that is able to adjust bias control signal 637 in a mannerthat matches the response of level detector 605 to the bias variationrequired by the active stages whose bias is being reactively controlled.

For example, bias adjustment circuit 607 can be bias conditioner 205 asshown in FIG. 2( a). As other examples, bias adjustment circuit caninclude circuitry that conditions bias control signal 636, scales it,compares it against a reference level, samples and holds it, sums a heldlevel with a variable level, or any combination of these. It can alsoinclude circuitry that monitors feedback on the actual level of one ormore of the reactive bias levels so as to provide improved control overbias.

Bias adjustment circuit 607 can also include circuitry that compensatesfor threshold variations of active devices within the reactive biasingsystem, including but not limited to variations in the threshold of itsfield effect transistors (FETs). Because the linear range of a FET maybe narrow, it may be important to calibrate or set the levels used so asto maintain the circuit's operation within that linear range.

Alternatively, bias adjustment circuit 607 can be eliminated orsimplified. This can apply if level detector 606 has a relatively strongsignal (such as an IF signal) to work with and is thus able to produce abias control signal of a suitable level and range of variation for biasgenerators 612 through 615 to work with directly.

First bias generator 612 can produce first bias level 632 according toadjusted bias control signal 637 and, optionally, according to a firstregulating feedback signal that is internal to first bias generator 612.Similarly, second bias generator 613 can produce second bias level 633according to adjusted bias control signal 637 and, optionally, a secondregulating feedback signal that is internal to second bias generator613. Similar principles apply to bias generators 614 through 615.

Bias generators 612 through 615 can be any circuits that are able toproduce a bias level that varies within a suitable range according toadjusted bias control signal 637 or bias control signal 636. Asexamples, they can be (as shown in FIG. 2) bias generator 203 usingvariable resistance 204-A, 204-B or 204-C.

In other embodiments of the invention each bias generator can have acorresponding bias adjustment circuit. Alternatively, two or more biasgenerators could operate from a first bias adjustment circuit and otherbias generators can have one or more other bias adjustment circuit orcan directly use bias control signal 636 and thus not need a biasadjustment circuit.

The series of commonly controlled reactively biased amplifiers as shownin FIG. 6 can provide substantial reductions in the use of receiverpower in some signal environments. It has fewer components and thus lessmanufacturing costs, compared with the self-adjusting amplifier stagesshown in the previous figure, It has less complexity, and thus is easierto test and less prone to failure. Its only level detector is locatedafter multiple stages of amplification, thus its bias conditioner maynot need to include active amplification because it has a relativelystrong signal to work with. Also, it may consume less power because ofonly having one level detector 606, only having one bias adjustmentcircuit 607 or not requiring amplification to condition the bias controlsignal.

The amplifier of FIG. 6 may be appropriate where RF or other earlyfiltering is not effective to attenuate jamming signals. This amplifiermay also be appropriate for applications where it is undesirable to addthe cost, complexity and power consumption of making each stage selfadjusting—that is, of having each amplification stage have its owndedicated level detector and perhaps its own dedicated bias adjustmentcircuit.

One skilled in the art will be easily able to determine the designdetails of a receiver that is a hybrid of the self-adjusting stages ofFIG. 5 and the commonly controlled stages of FIG. 6. For example, onebias control signal could be used for two or more amplifier or otheractive stages while self-adjusting bias control could be used for otheractive stages. Further, such a multi-stage receiver could also includeactive stages with fixed bias levels.

FIG. 7 is a functional block diagram, according to one embodiment of theinvention, of receiver front end 700 in which both a filter and an RFamplifier are optionally included in the receiver's signal path orswitched out of it. Receiver front end 700 receives RF input signal 720and produces IF output signal 732.

As shown, receiver front end 700 has two stages of active circuitry,each with a reactively adjusted bias under common control, and oneswitch. However, other embodiments can have more switches, more or feweractive circuit stages, or some of the active circuits can have a fixedrather than a reactively adjusted bias, or some of the active circuitscan have a self-adjusting bias.

Low noise amplifier 701 amplifies RF input signal 720 into firstinternal RF signal 721. The bias of low noise amplifier 701 can be setby first bias level 729, which can be produced by first bias generator709. Low noise amplifier 701 can be any type of RF amplifier withcharacteristics suitable for the particular application. For example, itcan be RF amplifier 201 as shown in FIG. 2( a).

RF switch and bypass circuit 702 receives first internal RF signal 721and produces switched RF signal 725. When in bypass mode, i.e. whenbypass,control signal 731 is asserted, switched RF signal 725 issubstantially first internal RF signal 721, though some switching lossmay occur within RF switch and bypass circuit 702. When bypass controlsignal 731 is not asserted, switched RF signal 725 can be the result offiltering first internal RF signal 721 by first filter 703 andamplifying the result by RF amplifier 704. Alternatively, switched RFsignal 725 can be the result of amplifying first internal RF signal 721by RF amplifier 704 and filtering the result by first filter 703.

RF switch and bypass circuit 702 can be any circuit able to transfereither first internal RF signal 721 or fourth internal RF signal 724 toswitched RF signal 725. Further, it is preferably a circuit able totransfer first internal RF signal 721 to either second internal RFsignal 722 or to switched RF signal 725 but not to both, so as to notunnecessarily load first internal RF signal 721 when operating in bypassmode.

First filter 703 receives second internal RF signal 722 from RF switchand bypass circuit 702 and produces third internal RF signal 723. Firstfilter 703 can be any circuit able to reduce undesired or jammingcomponents of second RF signal 722. In some embodiments, receiver frontend 700 is used in a transceiver device and first filter 703 is atransmission blocking filter.

RF amplifier 704 amplifies third internal RF signal 723 into fourthinternal RF signal 724. The bias of second RF amplifier 704 can be setby second bias level 730, which can be produced by second bias generator710. Second RF amplifier 704 can be any type of RF amplifier withcharacteristics suitable for the particular application. For example, itcan be the RF amplifier shown in FIG. 3.

In some embodiments of the invention, second filter 705 receivesswitched RF signal 725 from RF switch and bypass circuit 702 andproduces fifth internal RF signal 726. In other embodiments, there is nosecond filter and switched RF signal 725 is directly provided to RF toIF converter 706 and level detector 707. Second filter 705 can be anycircuit able to reduce undesired or jamming components of switched RFsignal 724. In some embodiments, receiver front end 700 is used in atransceiver device and second filter 705 is a transmission-blockingfilter.

RF to IF converter 706 converts fifth internal RF signal 726, orswitched RF signal 725, into internal IF output signal 732. RF to IFconverter 726 can be any type of RF to IF converter or mixer withcharacteristics suitable for the particular application.

As shown in FIG. 7, level detector 707 receives fifth internal RF signal726, or switched RF signal 725. It detects the signal level of thissignal, and thus indirectly it detects the signal level of RF inputsignal 720. In other embodiments, level detector 606 can receive asignal that is intermediate between RF input signal 720 and switched RFsignal 725, or it can receive IF output signal 732. According to thissignal level, level detector 707 produces bias control signal 727 andbypass control signal 731.

Level detector 707 can be any type of circuit that is able to detectchanges in the average input and output signal levels that occur over asuitable time frame. In particular, bias control signal 727 can begenerated by level detector 202 as shown in FIG. 2( a), and bypasscontrol signal 731 can be generated by comparing bias control signal 727against a threshold.

Bias adjustment circuit 708 produces adjusted bias control signal 728according to bias control signal 727. Bias adjustment circuit 708 can beany circuit that is able to adjust bias control signal 727 in a mannerthat matches the response of level detector 707 to the bias variationrequired by the active stages whose bias is being reactively controlled.

For example, bias adjustment circuit 708 can be bias conditioner 205 asshown in FIG. 2( a). As other examples, bias adjustment circuit caninclude circuitry that conditions bias control signal 727, scales it,compares it against a reference level, samples and holds it, sums alevel held with a variable level, or any combination of these. It canalso include circuitry that monitors feedback on the actual level of oneor more of the reactive bias levels so as to provide improved controlover bias.

Bias adjustment circuit 708 can also include circuitry that compensatesfor threshold variations of active devices within the reactive biasingsystem, including but not limited to variations in the threshold of itsfield effect transistors (FETs). Because the linear range of a FET maybe narrow, it may be important to calibrate or set the levels used so asto maintain the circuit's operation within that linear range.

Alternatively, bias adjustment circuit 708 can be eliminated orsimplified. This can apply if level detector 707 has a relatively strongsignal (such as an IF signal) to work with and is thus able to produce abias control signal of a suitable level and range of variation for biasgenerators 709 and 710 to work with directly.

First bias generator 709 can produce first bias level 729 according toadjusted bias control signal 728 and, optionally, according to a firstregulating feedback signal that is internal to first bias generator 709.Similarly, second bias generator 710 can produce second bias level 730according to adjusted bias control signal 728 and, optionally, a secondregulating feedback signal that is internal to second bias generator710.

Bias generators 709 and 710 can be any circuits that are able to producea bias level that varies within a suitable range according to adjustedbias control signal 728 or bias control signal 727. As examples, theycan be (as shown in FIG. 2) bias generator 203 using variable resistance204-A, 204-B or 204-C.

In other embodiments of the invention each bias generator can have acorresponding bias adjustment circuit.

Code division multiple access (CDMA) receivers can include a receiverchain that includes a low-noise amplifier (LNA) that can be bypassed bya switch, followed by a transmission rejection filter, followed by an RFamplifier that can be bypassed by a switch.

In cellular phone applications, it is important that the volume levelthe user perceives not vary with signal strength. To meet this need, thegain of the receiver chain, and sometimes the gain of the subsequentdemodulation and audio amplification, can be relatively preciselycalibrated by digitizing a signal that represents the current signalstrength into an 8-bit signal strength value representing, for example,signal strengths ranging from −106 to −21 dBm. This signal strengthvalue can be used as an index into a lookup table, each entry of whichrepresents a calibration factor that is used to control the gain. Such alookup table apparatus is called a “linearizer” because it corrects forthe non-linearity of the automatic gain control (AGC) level versus thereceived signal strength level.

When one of the amplifiers in the receiver chain is bypassed, thelinearizer curve should be shifted by the change in gain due tobypassing the amplifier. To continue with the above example, bypassingan amplifier results in the low end of the linearizer curve shiftingfrom −106 dBm to −106 plus the change in gain.

This change in gain can be estimated as follows: Each amplifier can havea gain of, for example, 15 to 16 dB. There can be some loss in thebypass path, for example 0.5 dB or more. Also, there is typically 1 dBuncertainty in the calibration process, which should be added here asmargin. This results in the end of linearizer curve being−106+15.5+0.5+1=−89 dBm.

A proposed extended jamming signal test calls for a desired signalhaving a strength of −90 dBm that is concurrent with a two-tone jammingsignal having a signal strength of −32 dBm for each tone.

This test can present a problem for the receiver if it is unable tooperate with one of the amplifiers bypassed. Specifically, the linearityor IIP³ of the RF amplifier must be significantly higher than if the RFamplifier is bypassed at the operating point (i.e. signal strength)corresponding to this test.

Qualitatively, not only does the second amplifier contribute its ownnon-linearity to the chain, it amplifies the undesirable effects of thenon-linearity of the first amplifier. Quantitatively, this difference inIIP³ can be required can be roughly estimated as equivalent to the gainthat could be bypassed.

However, bypassing either the LNA or the RF amplifier can present aproblem if the operating point of interest falls off the linearizer;that is, if there is no entry in the look-up table for the correspondingdigital strength value.

A first approach to dealing with this problem of is to automatically putback in the gain, i.e. switch back in the amplifier. This raises thereceived signal back into the range where the linearizer can compensatefor non-linearity at the operating point of interest. This approachprevents the receiver from operating with either of its amplificationstages bypassed when such operation would result in the digitized signalstrength being below the end of the linearizer table.

A drawback of this first approach is that having both amplifiersswitched in can significantly increase the linearity requirement thatthe second amplifier must meet, as discussed above.

A second approach is to move the transmission rejection filter into thebypass path. Using this architecture, the point at which one of theamplifiers is switched in and out, i.e. the bypass point can be loweredto the insertion loss of this filter, which can be about 2 dB, forexample. This can allow the bypass point to be about −91 dBm. Such abypass point can be less than the −90 dBm extended jamming signal testdescribed above.

Using the second approach can facilitate the goal of switching out oneof the amplifiers for this test. That is, bypassing the filter allowsthe IIP³ of the second stage amplifier to be significantly lower.

Another advantage of the second approach, and of the lower bypass pointthat it enables, is that in actual operation of the receiver one of theamplifiers is likely to be bypassed for a greater portion of theoperating time. The power consumed by the amplifier can be reduced oreliminated when it is unused. This can further save power and prolongbattery life.

TABLE 4 Breakdown of IS-95 J-STD-018 CDMA RX inter-modulationperformance specs input CDMA Level (dBm) input tone level (dBm) # oftones −101 −30 1 −101 −43 2 −90 −32 2 −79 −21 2

In the following table, the RF amplifier state is decided upon the CDMAsignal level being above or below the switch point. Case 1 is a switchpoint less than −90 dBm, Case 5 is a switch point greater than −90 dBm.

TABLE 5 Breakdown of IS-95 J-STD-018 CDMA RX inter-modulationperformance specs input tone level Case input CDMA level (dBm) (dBm) RFAmp State 1 −90 −32 Bypassed 2 −101 −43 Engaged 3 −79 −21 Bypassed 4−101 −30 Engaged 5 −90 −32 Engaged

Considering the input level upon each device given generates thefollowing table. 3 dB insertion loss and 50 dB transmission rejectionwas used for the duplexer. 2 dB insertion loss and 25 dB transmissionrejection was used for the transmission rejection filter. IIP³ can becalculated by the well-known formula IIP3=½(3*Tone level-Intermodulationproduct level). IIP³'s were calculated for an intermodulation productlevel marginally acceptable for demodulation of the CDMA signal. IIP³for cross-modulation with the transmission leakage and a single-tone isa phenomena best predicted by measurement and simulation. In some casesboth inter-modulation and cross-modulation contribute to raise therequired IIP³ greater than one type alone. Gain used for the LNA was 16dB, 15 dB for the RF amplifier, and 1 dB loss for the switches. Detectorlevels are increased by 3 dB in the cases of the two equal level jammingtones contributing.

TABLE 6 Linearity requirements for each of the stages vs cases anddetector level (all levels dBm) Case LNA IIP3 RF Amp IIP3 Mixer IIP3Detector level 1 −4.5 Bypassed 10.5 −15.5 2 1.5 −2.7 12.3 −13.2 3 3.5Bypassed 18.5 −6 4 8.0 −1.0 14.0 −3.9 5 −4.5 6.5 21.5 −3.0

It is evident that not bypassing the RF amplifier in Case 5 creates amuch higher demand for IIP³ from the RF amplifier and the mixer. Thesecond highest demand for the mixer comes from Case 3 in whichcross-modulation from the transmitter plays no part, which shows therewas no performance degradation due to having the transmission rejectfilter in the bypass path.

FIG. 8 is a circuit diagram for an embodiment of the invention that usesa sample and hold circuit to improve the accuracy and effectiveness ofthe reactive bias function by compensating for variations of circuitcomponents, operating conditions or both. These variations include butare not limited to variations in the thresholds of the field effecttransistors (FETs) used. The range of linear operation of a FET can benarrow and its threshold voltage (and thus the point at which it doesoperate linearly) can be affected by manufacturing tolerances,temperature variations or voltage fluctuations. Thus, it can beadvantageous to dynamically compensate for such variations, particularlywhen done as the same time as dynamically compensating for the signalstrength of the receiver's current operating environment.

In the example circuit diagram of FIG. 8, RF amplifier 801 can beequivalent or identical to RF amplifier 201 as shown in FIG. 2. Detector802 can be a minor variation (i.e. adding R20) from detector 202 asshown in the same figure.

The function of bias generator 803 is similar to that of bias generator203 as shown in the same figure, but it alters the bias of RF amplifier201 by changing the bias current level, while the bias voltage levelremains substantially constant. To implement this, the variableresistance circuit within bias generator 803 is moved to the bottomportion of bias generator 803. Another difference is that in biasgenerator 803 when shutdown signal 851 is asserted, all bias voltage andcurrent is shut off to RF amplifier 801.

These variations between bias generator 203 and 803 are independent ofthe threshold compensation feature of receiver 800; athreshold-compensating receiver could be designed using bias generator203 or a range of similar circuits.

The bias adjustment function is performed by bias level comparator 810,sample and hold circuit 811 and bias difference circuit 812.

Bias level comparator 810 can be any type of circuit that is able togenerate regulating feedback signal 842. In particular, comparing areference voltage against a signal internal to bias generator 803 cangenerate regulating feedback signal 842. In the embodiment shown, thereference voltage is formed by a two-resistor voltage divider betweenVcc and ground, which helps compensate for variations in Vcc.

Sample and hold circuit 811 can be any type of circuit that is able tosample regulating feedback signal 842 when the signal environment inwhich the receiver is sufficiently quiescent, and hold that signal valuewhen the signal environment is stronger. In the embodiment shown, whenbias control signal 840 is below a threshold set by detector referencesignal 850 then the current value of regulating feedback signal 842 issampled or transferred onto capacitor C20, and when above then the valueis held on C20.

Bias difference circuit can be any type of circuit that appropriatelyadjusts bias control signal 840 into adjusted bias control value 841.The adjustments can include but are not limited to generating thedifference between bias control signal 840 and the value being sampledvia capacitor C20 or held on capacitor C20.

FIG. 9 is a circuit diagram and a pin out diagram of an applicationspecific integrated circuit (ASIC) for bias control according to oneembodiment of the invention. As shown, many of the electronic circuitcomponents of FIG. 8 are formed within a single integrated circuithaving 10 pins. Implementing these circuit components as an ASIC canreduce manufacturing costs and complexity of receivers that usereactively biased front-end circuits.

It will be obvious to one skilled in the art that there are numerousother selections of what circuit components within FIG. 8, or withinanother embodiment of the invention, can be integrated. For example, an8-pin embodiment can be designed that omits the Bias Adjustment andShutdown signal pins.

FIG. 10 shows the functional components and their interconnections foranother embodiment of the invention. This embodiment is the first stagesof a receiver that uses the integrated circuit of the previous figure tobuild a receiver that can be operated in several modes used in mobiletelephone applications. These modes include analog modes such ascellular and advanced mobile phone service (AMPS) as well as digitalmodes such as code division multiple access (CDMA) and personalcommunication service (PCS).

Reactively biased front end circuits according to the present inventioncan be used within various types of mobile telephone receivers, as canswitching in and out the transmission rejection filter when the secondstage RF amplifier is switched in and out.

In the example shown in FIG. 10, antenna 1001 provides, via diplexer1002, an RF signal to both PCS duplexer 1003 and cellular duplexer 1004.PCS duplexer 1003 and cellular duplexer 1004 respectively provide RFsignals to PCS low noise amplifier (LNA) 1005 and cellular LNA 1006.They in turn respectively provide RF signals to optional transmissionrejection filters 1007 a and 1007 b, which in turn provide RF signals toswitch SW1.

SW1 determines whether the RF signal currently of interest (e.g. PCS orcellular) passes through transmission rejection filter 1007 c and secondstage RF amplifier 1008 prior to going on to switch SW2. Transmissionrejection filter 1007 c, which is optional, is a dual band filter, inthat its filtering applies to both cellular and PCS signals.

Switch SW2, in conjunction with SW1, selects the signal of interest andpasses it on to RF to IF converter 1009. Local oscillator 1010 providesthe intermediate frequency signal to RF to IF converter 1009.

Switch SW3 routes the output of RF to IF converter 1003 on either toAMPS SAW filter 1011 or to CDMA SAW filter 1012.

Local oscillator rejection filter 1013 attenuates the local oscillatorsignal from entering level detector 1014. Level detector 1014 producesdetect and hold signal 1041. Bias Asics 1015 to 1017 use detect and holdsignal 1041 to generate the bias levels for their respective activecircuits.

The bias of PCS low noise amplifier 1005 and of cellular amplifier 1006is reactively set by bias ASIC 1011 according to detect and hold signal1041. The bias of second stage RF amplifier 1008 is reactively set bybias ASIC 1016 according to detect and hold signal 1041. Similarly, thebias of local oscillator 1010 is reactively set by bias ASIC 1017according to detect and hold signal 1041.

FIG. 11 demonstrates the reactive bias function applied to a single-bandCDMA super-heterodyne receiver. The incoming signal is received at theantenna 1101, and the duplexer 1102, separates the outgoing transmissionfrom the incoming receive signal. The receive signal is then passed tothe LNA 1103, which can be bypassed and shut off by switch 1116 and biascontrol circuit 1113 respectively, via control signal Mode 1. The outputof the LNA 1103 is passed to the RF filter 1104 and then to the RF Amp1105. The bias control of the RF Amp may benefit from direct knowledgeof the first state being bypassed, rather than only relying on thedetector power decrease to lower the bias. This implementation showsthat both the RF filter 1104 and RF Amp 1105 can be bypassed by theswitch 1115 via control signal Mode 2, effectively lowering the power atwhich the RF Amp can be bypassed and shut off. The output of the RF Ampis passed to the mixer 1106, which down converts the RF signals to IF.From the mixer the IF signals are passed through the IF SAW filter 1107,which limits the spectrum only to the channel BW that contains thesignal of interest.

The RF input spectrum to the mixer is also sent to a power detector viaa tap 1109, which could be a directional coupler, filter, matchingnetwork, or combination thereof. The primary concern is to detect thespectrum of signals experienced by the preceding amplifiers, and avoidany LO leakage that could be detected inadvertently. The filtering inthe tap 1109, depends on the LO rejection of the mixer. The spectrumpassing through tap 1109 feeds the detector 1110, which passes a dcsignal corresponding to the total signal power to comparator 1111, whichcompares the detector output with a detector reference level todetermine if the incoming signal power is large enough to increase thebias of the LNA 1103, RF Amp 1105, and LO Buffer 1108 via bias controlcircuits 1113, 1112, and 1114 respectively. It is also possible to tapthe IF signal after the mixer 1106 and achieve the same result bydetecting the signal power in the IF spectrum, but a key point is thatthe detector 1110 taps the signal before the band limiting IF SAW 1107,which would strip off any jammers experienced by the front endamplifiers.

FIG. 12 demonstrates the reactive bias function applied to a CDMA directconversion receiver. The front-end amplifier architecture is similar tothat of FIG. 11, except it shows the addition of some programmable gaincontrol (AGC) of the LNA to compensate for the lack of an IF AGC. Thedown converting mixer(s) 1209 is the most critical element in the directconversion architecture, requiring superior LO rejection to prevent theLO signal from leaking back into the RF path. To minimize the potentialfor LO leakage, the LO is divided down to a quadrature LO by the divideby two 1207 and the phase shift 1206 at the last possible point. The LObuffer 1208 buffers a signal at twice the RF frequency preventing anydisturbance to the RF path. It is interesting to note that by biasingdown the LO buffer, it could be possible to reduce leakage at lowersignal levels depending on the design of the divide by two 1207. As aresult of the increased LO rejection requirements of the mixer, thedetector 1210 does not require an LO reject filter on the tap of themixer input spectrum. It may be desirable to implement a power leveldetector after the quadrature down conversion due to the very lowfrequency content—however, any dc offsets could present a challenge ifnot properly compensated for at the detector output.

Another method to implement the reactive biasing function is shown asthe digital bias controller 1213. One method may be to sample thedetector output using an A/D converter, in which a comparison with thedetector reference could be implemented digitally. A look-up table (LUT)can be constructed to provide any bias versus detected power functiondesired. Other look-up tables can be constructed to serve programmablebias controllers for the RF amplifier and LO buffer off the same A/Doutput. This strategy could be used in conjunction with user controlledprogrammable bias without much additional design effort.

Yet another variation of the bias feedback loop would be to have A/Dconverters sample the I/Q outputs of the mixer(s) 1209 directly, beforeany filtering is applied. Aliasing and overdriving the inputs of suchAND converters would not be an issue since only a moving average of thepower is desired, and the lower range of sensitivity of the A/Dconverters would be set at a relatively high signal level correspondingto about −55 dBm at the input. A dynamic range as small as 25 dB wouldbe sufficient to obtain enough resolution to optimize the currentsavings of the biasing versus input signal power. Such an implementationcould replace the analog detector, comparator, and bias controllers witha digital signal-processing counterpart.

FIG. 13 demonstrates how reactive biasing can be effective againstdistortion before it occurs. On the right hand side is a possiblespectrum corresponding to each stage of the receiver on the left.Signals within the RF system BW as defined by the duplexer 1302 passunfiltered into the LNA 1303. The example input spectrum 1309demonstrates a small signal of interest surrounded by much strongerjamming signals. The input spectrum is amplified by the LNA 1303 and RFAmp 1305, but not selectively filtered by filter 1304 since it alsospans the RF system BW. The detector 1306 is exposed to a similar signalenvironment as the front-end amplifiers and so can distinguish a strongsignal environment amid the weak signal of interest. In this example,the LO frequency is equal to the RF frequency 1311 as in directconversion. In a superheterodyne receiver the LO would be offset by theIF frequency. In both cases after down conversion a band-limiting filter1312 removes most of the original jamming energy, leaving only thesignal of interest 1313 and any in-band distortion created by thestronger signals. The resulting spectrum 1313 is what is used forReceive Signal Strength Indication (RSSI) 1314, which is used todetermine when to bypass the LNA and/or RF Amp at the front end. TheRSSI, since it is derived from a band limited signal, has is unconnectedto the spectrum that can create the distortion and so it cannot make anyadjustments to prevent the distortion. The detector 1306, on the otherhand, can sense an increasing jammer environment and adjust the bias ofthe front-end amplifiers accordingly before any significant distortionscan occur.

FIG. 14 is a plot representing the current consumption versus RX powerfor the different modes using reactive bias. The horizon line in theback (S1) represents the peak bias condition under a very strongdetected power. This is representative of the bias of the present stateof the art CDMA receivers used. Reactive bias allows this current to begreatly reduced with reduced jammer power as demonstrated by the reducedcurrent as one moves from S1 to S16 in the foreground. Below thedetector threshold the bias is at a minimum. Moving from left to rightalong the RX Power axis, the first and highest current state wouldrepresent both the LNA and RF Amp being engaged. The next staterepresents the RF Amp being bypassed, reducing the peak currentconsumption. The right most state is with both the LNA and RF Ampbypassed. Even with no jammer power, as the signal of interest increasesit will be detected and increase the bias level of the LO buffer.Similarly, at very low RX Power, the high TX level can leak intoreceiver enough to be detected raising the bias level even with noexternal jammer present.

One skilled in the art will be easily able to determine how stages andcircuits within the front end of a receiver other than those expresslydiscussed herein could be designed with reactive biasing in accordancewith the principles, spirit and scope of the invention.

As illustrated herein, the invention provides a novel and advantageousmethod and apparatus for the front-end stages of a receiver withreactively biased amplification, oscillation and other circuits toprovide low power, high linearity and low intermodulation. One skilledin the art will recognize that one may employ various embodiments of theinvention, alternative designs for the invention and changes in its formand detail. In particular, the circuits shown in FIGS. 2, 3, 4, 8 and 9may be simplified, augmented or changed in various embodiments of theinvention. Also, the amplifiers of FIGS. 5, 6, 7 and 10 may beintermixed, extended to more stages, simplified, augmented or changed.

Such changes and other changes do not depart from the principles orspirit of the invention, the scope of which is set forth in thefollowing claims.

1. A receiver for radio frequency communications, comprising: anamplifying circuit receiving a radio frequency input signal, wherein theamplifying circuit has an adjustable bias level; any number of bypassswitches coupled across the amplifying circuit; and baseband circuitrycoupled with at least one of the any number of bypass switches, whereinthe baseband circuitry generates a bypass control signal to control theat least one bypass switch so as to vary a bias control signal that isgenerated to set the adjustable bias level of the amplifying circuit;wherein the at least one bypass switch provides a direct connectionbetween a low noise amplifier and a mixer when utilized according to thebypass control signal.
 2. The receiver according to claim 1, furthercomprising: a bias generator coupled with the amplifying circuit,wherein the bias generator generates at least the bias control signalbased on a signal dependent on a total received radio frequency power ofthe radio frequency input signal to set the adjustable bias level of theamplifying circuit.
 3. The receiver according to claim 2, wherein thebias generator comprises a circuit selected from an RSSI circuit.
 4. Thereceiver according to claim 3, wherein the configuration of the biasgenerator is selected from a configuration that conditions the biascontrol signal, a configuration that responds to bias level asregulating feedback, and a configuration that holds the bias level at aparticular level.
 5. The receiver according to claim 1, wherein the atleast one bypass switch minimizes oscillator self mixing, receiversignal self mixing and oscillator leakage.
 6. The receiver according toclaim 1, wherein the amplifying circuit comprises a first filter coupledwith a radio frequency amplifier, wherein the radio frequency amplifierhas the adjustable bias level to generate an internal signal accordingto the bias control signal.
 7. The receiver according to claim 6,further comprising: a oscillation signal; a dividing circuit thatreceives the oscillation signal and divides down the oscillation signal,wherein the divided down oscillation signal is applied to the mixer. 8.A radio frequency circuit, comprising: an amplifying circuit receiving aradio frequency input signal, wherein the amplifying circuit has anadjustable bias level; a bias control generator coupled with theamplifying circuit, wherein the bias control generator provides a biascontrol signal to control the adjustable bias level of the amplifyingcircuit and to control a first internal signal; and a bypass switchcoupled across the amplifying circuit, wherein the bypass switchreceives the radio frequency input signal and provides a directconversion of the radio frequency input signal to the first internalsignal.
 9. The receiver according to claim 8, wherein the bypass switchprovides the direct conversion of the radio frequency input signal tothe first internal signal wherein the first internal signal comprises aDC component signal corresponding to a bias power received by theamplifying circuit.
 10. The receiver according to claim 9, wherein theamplifying circuit is selected from an amplifier, a low noise amplifier,a linear amplifier, a mixer and a radio frequency converter to convertintermediate frequencies.
 11. The receiver according to claim 8, whereinthe bias control generator comprises a circuit selected from an RSSIcircuit.
 12. The receiver according to claim 11, wherein theconfiguration of the bias control generator is at least in part selectedfrom a configuration that conditions the bias control signal, aconfiguration that responds to bias level as regulating feedback, and aconfiguration that holds the bias level at a particular level.
 13. Thereceiver according to claim 8, wherein the bias control generatorcomprises a detector configured to receive a signal indicating a signalstrength of the radio frequency input signal and to produce accordingthereto the bias control signal, where the bias control signal isdependent on a RSSI dependent on baseband circuitry which includes afeedback power detection.
 14. The receiver according to claim 13,wherein the bypass switch minimizes oscillator self mixing, receiversignal self mixing and oscillator leakage.
 15. The receiver according toclaim 13, wherein the bias control generator further comprises a biasadjustment circuit comprising a circuit selected from an operationalamplifier circuit and sample and hold circuit.
 16. The receiveraccording to claim 13, wherein the bias control generator furthercomprises a digital bias controller coupled with the detector, whereinthe digital bias controller samples an output of the detector andcompares the sampling with a reference.
 17. The receiver according toclaim 16, wherein the bias control generator comprises a detectorcoupled with the radio frequency to intermediate frequency converter,such that the detector receives a level of the intermediate frequencyoutput and produces the bias control signal according to the level ofintermediate frequency output.
 18. A method for amplifying a radiofrequency signal comprising: receiving a radio frequency input signal;amplifying the radio frequency input signal into an output signalincluding adjusting the amplification of the radio frequency inputsignal into the output signal according to an adjustable bias level anda feedback power signal; generating a bias control signal based at leastin part on the radio frequency input signal; controlling the adjustablebias level according to the generated bias control signal; switching theinput radio frequency signal to the output signal to correspond to astrength of the feedback power signal including bypassing filtering inthe switching of the input radio frequency signal to the output signaland establishing direct conversion between the radio frequency signaland the output signal.
 19. The method of claim 18, further comprising:detecting a base-band signal; and generating the bias control signalbased at least in part on the detected baseband signal.
 20. The methodof claim 18, wherein the amplifying occurs in a singular step whereinsaid singular step having a plurality of bias levels.